The present invention relates to mass spectrometry and, more particularly, to the scheduling of the steps involved in performing mass spectrometry. The present invention will be of particular benefit to types of mass spectrometry that generate large quantities of data and hence give rise to lengthy data-processing. Examples of data-rich spectrometry include quadrupole time of flight (QTOF), nuclear magnetic resonance (NMR) and Fourier transform Orbitrap (FT-O). Details of an Orbitrap system can be found in U.S. Pat. No. 5,886,346.
High-resolution mass spectrometry is widely used in the detection and identification of molecular structures and the study of chemical and physical processes. A variety of different techniques are known for the generation of mass spectra using various trapping and detection methods. The present invention is applicable to many of these techniques.
One such technique is Fourier Transform Ion Cyclotron Resonance (FT-ICR). FT-ICR uses the principle of a cyclotron, wherein a high-frequency voltage excites ions to move in a spiral within an ICR cell. The ions in the cell orbit as coherent bunches along the same radial paths but at different frequencies, the frequency of the circular motion (the cyclotron frequency) is proportional to the ion mass. A set of detector electrodes are provided and an image current is induced in these by the coherent orbiting ions. The amplitude and frequency of the detected signal are indicative of the quantity and mass respectively of the ions. Mass and frequency spectra are obtainable by carrying out a Fourier Transform of the ‘transient’, i.e. the signal produced at the detector's electrodes.
FIG. 1 shows a known mass spectrometer 10, that is operated as follows. Samples are prepared in an optional sample preparation stage 12 with ions being generated in an ion source 14 before being stored in an ion trap 16. When desired, the ions are transmitted to an ion cyclotron resonance (ICR) cell 20 via ion optics 18. The ion transmission and capture in the ICR cell 20 can occur via two well-known schemes: gated trapping or continuous trapping. The ions in the ICR cell 20 are excited by a radio-frequency signal provided by an excitation system 22 operated under the control of a distributed computer system 26. The transient is detected by detection hardware 24 (amplifiers and other analog circuitry) before being digitized at 28 and passed to the control computer 30. When a complete signal has been detected by the hardware 24, the transient data are either sent directly to the user data system 32 for storage or is processed by the control computer 30 to produce frequency or mass spectra peaks lists. Any combination of transient data can be displayed. In addition, simple decisions for controlling the next data acquisition cycle are possible where the transient data are processed. A more detailed description of an FT-ICR spectrometer can be found in our co-pending Patent Application No. GB0305420.2.
The method of operation of the mass spectrometer of FIG. 1 can be simply summarized as shown in FIG. 2. The steps are as follows:                (i) ionization in the ion source at 34;        (ii) ion collection and preparation in the ion trap at 36;        (iii) ion transmission to the ICR cell at 38;        (iv) ion detection in the ICR cell (i.e. transient data collection) at 40;        (v) processing of the transient data at 42; and        (vi) storage of the processed data at 44.        
Once storage step 44 has been completed, a new cycle may begin with ionization step 34 followed by sample preparation step 36 as possibly modified by the results of the transient data processing step 42 of the previous cycle. Often, the processing step at (v) is omitted and instead the data collected at step (iv) is merely dumped direct to a computer disk. The time taken for each step/steps is shown in FIG. 2. As can be seen the longest steps are for data detection and data processing 40 and 42, and these steps are performed successively. This is because the data collected in one cycle, once processed, may be used to control the ion collection and preparation in the following cycle.